Question about GRC scope sink

Hi, I hve just a little question about GRC scope sink please
the question is I just generate the signal about 1.5Mhz amd Amplitude 1v
p-p directly trough the usrp
So i know that when i connect the usrp source to the scope sink i will
see the signal that it’s frequency is the difference of the input
frequency - nco frequency
but what is the Y axis that call counts measured for but i know that my
input is = 1vp-p but in the scope sink show about 3k(counts?) p-p what
is that?
thank you very much for yours advice